Ask HN: APIs for Music Play & Purchase?

I've long wanted to integrate various features into the products that I build that allow one to listen to a _and purchase_ a piece of music, while earning a commission on the sale. So far, I've come up empty handed in finding such a thing. Amazon MP3 doesn't seem to offer a listening API, YouTube doesn't offer a purchase API, iTunes doesn't seem to have any API, etc.

In a specific example, writers on [RolePlayGateway](http://www.roleplaygateway.com) often [associate theme songs with their characters](http://www.roleplaygateway.com/avalon-dawn-t78127-20.html#p1843788) or [pivotal moments in story](http://www.roleplaygateway.com/roleplay/the-multiverse/characters/joruv-komfeiv?start=0#roleplay2324177). Readers should be able to click a single button to play the full song while they read the post, and have the ability to purchase the track for their own library. Ideally, commission would be awarded for such purchases.

What APIs exist for easy search, play, and purchase of music?